Filling Large transom hole - options

[stevebrownell]

Any suggestions as to how to fill a large circular hole in the transom? My boat has an exisiting cutout about 4" round, half of which is below the waterline. Currently, there is a standard screw in deck plate holding back the sea....

Was thinking epoxy w. high strength filler, double up on a beveled piece of marine ply, wetted out, glassed, etc. It'll look like crap, but anything is better than the plastic that is there now. I do not plan on doing a transom replacement at this time, just want to plug the existing hole.